This invention relates generally to a method of repairing existing manholes and similar structures using elastomeric materials. More specifically, this invention relates to a method of repairing existing manholes and similar structures by applying a fast-curing elastomeric material using spray techniques whereby a homogeneous, non-porous, and monolithic coating or lining is formed. The fast-curing elastomeric material can be applied directly to existing concrete, brick, tile, mortar, and metal surfaces normally found in sewer manholes and catch basins, sewer and drainage pipes, parking decks, bridge piers and footings, holding ponds, bridge trusses, culverts, gratings, and the like and does not require any formwork. The elastomeric coatings of this invention provide effective surface protection against wear, corrosion, and water infiltration and can be applied in a single operation to horizontal, vertical, and overhead surfaces. The elastomeric materials used in the present invention are prepared by initiating the reaction of a isocyanate-terminated compound or polymer with an amine-terminated polymer or an aliphatic or aromatic diamine immediately before applying the elastomeric material to the surface to be coated. Preferably the reactive components (i.e., isocyanate-containing and amine-containing materials) are mixed directly in the spray gun used to apply the elastomeric material.
The repair and rehabilitation of the infrastructure in most of the industrialized world has become of increasing importance in recent years. The deteriorating infrastructure--including engineering structures such as sewer systems, water collection systems, bridges, culverts, catch basins, and the like--is becoming an ever increasing challenge to repair and maintain in a cost effective and timely manner. Of particular importance are the sewer systems--including both the lines and access manholes--in our older cities which may have been installed a century or more ago. Due to the location of many of these systems below ground, deterioration of the infrastructure is generally not readily apparent to the public until there is acute failure resulting in cracked pavement, collapsed streets, sewer backups, local flooding, low water pressure, or other severe problems. Also due to the underground location of these structures, complete replacement of the systems is very expensive as well as disruptive of human and economic activities above ground. If a sewer system is allowed to deteriorate until acute failures occurs, often the only method available to correct the problem is total replacement of the failed portion of the system. It is preferred, therefore, to apply preventive maintenance measures to such systems to prevent, or at least minimize, such acute failures and to maintain the operating capabilities of such systems. It is desirable, therefore, to provide methods by which such engineered structures can be repaired simply, effectively, with minimal downtime, and at a low-cost.
Several methods short of total replacement have been developed for tile repair or rehabilitation of existing structures such as sewer manholes. For example, U.S. Pat. No. 5,002,438 provides for the repair of existing manhole structures by the spray application of a cementitious mixture to the interior of the manhole structure to form a liner. Two to five hundred pounds of the cementitious mixture is generally required to repair a typical manhole structure. And such a liner can only be put back into service after the cement mixture sets. A booklet published by the U.S. Department of Housing and Urban Development entitled "Utility Infrastructure Rehabilitation" (Nov. 1984) ("Booklet") also presents several methods that are reportably useful in such rehabilitation efforts. These methods include (1) coatings (such as epoxy, acrylic, or polyurethane) applied to the interior walls of the manhole, (2) chemical grouts injected into the surrounding ground from the interior of the manhole, and (3) structural liners (e,g., a fiberglass liner) inserted inside the manhole. Booklet at 5-57 to 5-58. None of these methods have proven to be completely satisfactory. For example, although it is known to apply polyurethane coatings with a airless sprayer, the surface to be coated by be "very clean, free of debris, structurally sound, dry." Id. at 5-57. For structurally damaged or disintegrated manhole structures (i.e., the structures most in need of repair and most likely to be found in the sewer systems of our older cities), only the structural liners are reported to be useful. Id, at 5-59. Thus, additional methods are needed to repair and rehabilitate existing manholes, especially structurally damaged or disintegrated manhole structures. It would be desirable to provide a relatively simple and quick method for the repair or rehabilitation of both structurally sound manholes and structurally damaged or disintegrated manholes. It would also be desirable if such a method used a minimum of materials and if the repaired manhole could be returned to service almost immediately. It would also be desirable if such a method could be used on both the brick and mortar interior surfaces as well as on metal surfaces commonly found in manholes. The present invention provides such a method. Other advantages and benefits of the present invention will become apparent upon a review of the specification.